Justification:
Listed as Critically Endangered on the basis that its area of occupancy is a maximum of 9 km², but is likely to be considerably less than this and potentially less than 1 km², it has an extent of occurrence of around 16 km², the species has a severely fragmented population, and there is a continuing decline in both extent of occurrence and area of occupancy, as well as potentially in the number of subpopulations.

This gecko is endemic to Madagascar where it is known from a few localities in the extreme southeast of the island, at Ambatotsirongorongo (Ramanamanjato et al. 2002) and Sainte Luce (Ramanamanjato et al. 2002). A third population, at Petriky, was extirpated before 1994 as a result of habitat destruction (Ramanamanjato et al. 2002). At Sainte Luce, it is known from three forest fragments (Ramanamanjato et al. 2007). Its distribution within its extent of occurrence is discontinuous and it is absent from Mandena littoral forest, possibly because of the lack of suitable plant species.It is unlikely to occur outside this area, but may be present in littoral forests further north which have biological affinities to Sainte Luce. It occurs from sea level to 300 m asl. The species is unknown from the adjacent protected areas of Andohahela and Tsitongabarika. It has an extent of occurrence of 16 km². The area of occupancy may be as low as 1 km², and is certainly no greater than 9 km² as this represents the maximum extent of forest containing suitable plant species within its range.

Three subpopulations exist, two of which occur in forest fragments at Saint Luce (40% of the total population), with the remaining 60% in Ambatotsirongorongo. Due to the isolation of these sites from one another, the low dispersal capabilities of these lizards, and the small area of suitable habitat remaining to support each subpopulation (at most 9 km² between the three subpopulations), the population is considered to be severely fragmented. The total population is estimated to include between 5,000 - 10,000 individuals, with an estimated population density of approximately 10 individuals per hectare where suitable Pandanus plants are found (J.-B. Ramanamanjato pers. comm. January 2011). Due to the loss of the plants on which the species depends throughout its range, the population is in decline.

This day gecko is only known from low altitude littoral and transitional forests in the coastal forests of Tolagnaro, southeastern Madagascar. It can be found in degraded forest with a sufficiently dense canopy, but is absent from deforested areas and those where key plant species are absent. It is thought to have specific habitat requirements for egg-laying and usually uses a single species of Pandanus that is found at Ambatotsirongorongo and Sainte Luce (Jenkins et al. 2005). During the night and the day it uses Dypsis palms such as Sainte Luce Dypsis (D. saintelucei) and Ravenala madagascariensis to forage (Ramanamanjato et al. 2002).

This day gecko is threatened by the destruction of its remaining forest habitat and selective exploitation of Dypsis species by people. The screw palms (Pandanus spp.) on which this species depends are slow-growing, and so loss of these during land clearance represents a threat to this species. Although new protected areas have been created within its range, illegal forest degradation continues. Forest fragments in Sainte Luce where this species occurs are used by local communities for forest resources and although a local management law (dina) was passed in 2005, the forest remains under heavy pressure. Some areas of forest in Sainte Luce where this species occurs will be destroyed if planned ilmenite mining proceeds, which may result in the loss of up to 20% of the population.

The Ambatotsirongorongo forest and two of the fragments at Sainte Luce are being developed and managed as new protected areas. An estimated 80% of this species' population falls within protected areas, but information on the state of these forests and in particular the key plants that P. antanosy requires are lacking. The population of this species is presently being monitored, and small-scale captive breeding programs may be appropriate for this species. The protected population at Sainte Luce may be stable, as this area is subject to a conservation management plan. All species within the genus Phelsuma are included on CITES Appendix II.